Add clang-format check as part of the merge request pipeline

It would in general good to include clang-format check as part of the merge request pipeline to allow developer an easy way to notice if their format is not correct. Even with formatting deployed as part of the repo, it is easy to accidentally commit code with wrong formatting depending on the used IDE.

I have no strong opinions if this check should be a failing or non-failing one. Format check can run already early on as it does not have other requirements than having the repository cloned.